Spatial and temporal patterns of fertilization in black abalone (Haliotis cracherodii Leach, 1814): Analysis of surrogate gamete spawning experiments with application towards populations on San Nicolas Island, California

Abstract

The endangered black abalone (Haliotis cracherodii) suffered devastating losses along the coasts of Southern California, primarily caused by the effects of withering syndrome. Subsequent recovery may be hindered by the Allee effect, which limits the reproductive output when population densities are below a critical threshold and broadcast spawners are too distant for their gametes to mix in sufficient concentrations to result in fertilized eggs. I conducted simulated spawning experiments in two types of habitat on San Nicolas Island (SNI) in California using surrogate gametes to examine how proximity of spawning black abalone affects the fertilization potential, based on concentration of particles over distance and time. I found that habitat type is an important factor contributing to particle retention. With the linear design of the simulated spawning experiments, fertilization can still occur between black abalone located as far as 4 m apart in the crevice habitat. Nearest neighbor data, collected since 2005, were compared with 8-years of data on abalone abundance and microhabitat type during annual surveys in nine sites around the periphery of SNI to determine potential causes for the disparities in recovery rates among the study sites. Abalone density was examined since 2001 to count the number of patches, defined as groups of at least five abalone within a 2 x 4 m2 area along study transects. Annual population growth, number of patches, and the change in nearest neighbor distances show a direct correlation, consistent with the hypothesis that the Allee effect is responsible for the inconsistent recovery around SNI.